Ensure global defers run on exit (#173)

DESCRIPTION

@@ -44,7 +44,8 @@ Imports:
     graphics,
     grDevices,
     stats
-Suggests: 
+Suggests:
+    callr,
     covr,
     DBI,
     knitr,

NEWS.md

@@ -1,5 +1,9 @@
 # withr (development version)
 
+* Handlers registered with the global environment (as happens when `local_()` 
+  is run at the top-level, outside a function) are now automatically run
+  when the R session ends (#173).
+
 * New `with_language()` and `local_language()` to temporarily control the
   language used for translations (#180).
 

R/compat-defer.R

@@ -13,9 +13,11 @@ defer <<- defer <- function(expr, envir = parent.frame(), priority = c("first",
   if (identical(envir, .GlobalEnv) && is.null(get_handlers(envir))) {
     message(
       "Setting deferred event(s) on global environment.\n",
+      "  * Will be run automatically when session ends\n",
       "  * Execute (and clear) with `withr::deferred_run()`.\n",
       "  * Clear (without executing) with `withr::deferred_clear()`."
     )
+    reg.finalizer(envir, function(env) deferred_run(env), onexit = TRUE)
   }
   invisible(
     add_handler(

tests/testthat/_snaps/defer.md

@@ -4,6 +4,7 @@
       defer(print("howdy"), envir = globalenv())
     Message <simpleMessage>
       Setting deferred event(s) on global environment.
+        * Will be run automatically when session ends
         * Execute (and clear) with `withr::deferred_run()`.
         * Clear (without executing) with `withr::deferred_clear()`.
 

tests/testthat/test-defer.R

@@ -41,6 +41,17 @@ test_that("defer()'s global env facilities work", {
   expect_null(h)
 })
 
+test_that("defered actions in global env are run on exit", {
+  path <- local_tempfile()
+  callr::r(
+    function(path) {
+      withr::defer(writeLines("a", path), env = globalenv())
+    },
+    list(path = path)
+  )
+  expect_equal(readLines(path), "a")
+})
+
 test_that("defer executes all handlers even if there is an error in one of them", {
 
   old <- options("test_option" = 1)